Devices employing click discs as contact elements in an X-Y matrix of switch contacts have been known for a number of years. For example, such a device for use with an electronic calculator keyboard is described in U.S. Pat. No. 4,005,293 issued Jan. 25, 1977 in the name of Henry J. Boulanger and incorporated herein by reference.
My U.S. Pat. No. 4,392,181 issued July 5, 1983 and incorporated herein by reference discloses a click disc assembly comprising a planar molded plastic substrate and twelve contact dots of electroconductive ink arranged on such substrate in a 3.times.4 X-Y matrix consisting of four "X" rows of three contact dots each forming these "Y" columns. The dots in each of the four "X" rows are included in four corresponding paths of electroconductive ink deposited on the substrate and leading to four corresponding "row" terminal locations within a terminal region or zone at one end of the substrate. The dots in each row are thereby all electrically connected to a respective one of such locations.
Overlying the three "Y" columns of the matrix are three steel strips each having formed within its edges four click disks electrically connected to the edge portions of that strip and each disposed above a respective one of the four contact dots in that column. An insulating layer separates the strips from the paths on the substrate except in areas beneath the click discs where the layer has holes therein to permit the discs to contact their underlying contact dots. Each click disc by touching such dot electrically couples the "column" strip of which the disc is a part to the "row" electroconductive path of which the dot is a part. The edge portions of the three column strips extend to the mentioned terminal zone on the substrate to have end tabs overlying three corresponding "column" terminal locations in that zone.
Within that zone, and prior to formation of the electroconductive paths on the substrate, L-shaped metal terminal pieces are inserted into apertures in the substrate at the "row" and "column" terminal locations so that one of the "L" arms of each terminal passes with a press fit through and then beyond such aperture to end in a tip outwardly salient from the substrate. The other terminal arm or head of the terminal lies flat on the substrate's upper surface. After such inserting, the "row" terminals are bonded and electrically coupled to the "row" electroconductive paths by deposition of the electroconductive ink of these paths to cover the flat heads of such terminals. The "column" terminals are, on the other hand, bonded and electrically coupled to the "column" strips by welding the mentioned end tabs of such strip's through holes in the mentioned insulating layer to the flat heads of the "column" terminals. After the "row" and column terminals have been connected up as described in the click disc assembly, the outwardly projecting tips of the terminals are soldered to plated rectangular slots formed in a printed circuit card disposed below and spaced from the substrate board of the click disc assembly. In this manner, the X-Y switch contact matrix of such assembly is connected through the soldered terminals to operating circuitry on the printed circuit card to provide, say, a complete telephone dial unit.
My copending application Ser. No. 451,358 filed Dec. 20, 1982 and incorporated herein by reference discloses a click disc switch assembly differing from that disclosed in my U.S. Pat. No. 4,392,181 in at least the respects that the electroconductive conductors on the substrate are of copper so as to provide copper contact areas and pads (and, also, copper terminals on the edge of the substrate board), the click disc strips are secured by the welding of end tabs thereof to bonding pads forming parts of the copper paths on the substrate board, and the board has thereon a plurality of pairs of copper bars which are substantially of the same thickness as such copper paths, and which are disposed beneath the click discs to compensate for the effect on the "click feel" of the click discs of variations from nominal in the thickness of the contact areas on the board which are contacted by the click discs upon depression thereof.
While the last mentioned click disc assembly has been found to be quite satisfactory, it has the disadvantages of high cost to produce its copper paths on its substrate board. Too, the board must, in order to have such paths formed thereon, be made of a material which is relatively expensive and productive of more contamination than is desirable. Moreover, in the case of both the click disc assembly of my U.S. Pat. No. 4,392,181 and that of my application Ser. No. 451,358, the necessity for having the click disc strips secured to underlying parts of the assembly adds to the cost, effort and time involved in making the assembly.